Metallic garment accessories, such as elements for slide fasteners, snap buttons, and shell caps which are components of buttons are attached to clothes, bags and the like and form a part of their appearances. Therefore, high designability is required for the garment accessories, and the color tones presented by the garment accessories are one important factor for the designability. However, since the metallic colors of the base materials are limited, the metallic garment accessories are generally colored by painting, printing, plating and the like. However, the coloring by painting or printing may generally lose the metallic luster of the garment accessories. Special painting methods such as silver mirror coating finishing are also known in the art, but these methods are very expensive. Therefore, the plating (electroplating, electroless plating, substitution plating, chemical conversion treatment, etc.) is generally adopted in order to impart a metallic color different from that of the base material to the metallic garment accessory, and the metallic fastener elements, the snap buttons, the shell caps and the like are conventionally plated on their full surfaces by electroplating or chemical plating. For example, when the metallic fastener elements are plated, conductive fibers are woven in advance in fastener tapes to which the elements are attached, along the tape longitudinal direction, and a large number of elements are fixed to the fastener tapes by means of caulking such that the elements are brought into contact with the conductive fibers. Electricity is then applied to the conductive fibers while continuously passing the fastener tapes through a plating bath to cause cathodic polarization of the elements, thereby depositing the metal on the outer surfaces of the elements. However, this method takes labor for the reasons that adjustment is required such that the plating metal is not deposited on the conductive fibers, and the like, because the electric current is directly applied to the elements.
Recently, there have been demands for diversified and improved designability and fashionability in relation to the garment accessories. For example, there are needs for reversible fashions having glossy colors different between the front and back sides and for garment accessories having various glossy colors. However, in the plating method of the fastener tapes with the conductive fibers interwoven as stated above, it is difficult to perform one side plating. Further, if different colors are produced between the front and back surface or one side plating is carried out by the conventional plating method, for example, it is necessary to perform the plating while masking one of the front and back surfaces with a resin coating, then remove the mask, and optionally repeat the same process for the other of the front and back surfaces. However, such processes are unsuitable for the industrial production, because they take much labor and costs. In addition, since the shell cap is a part to be attached to the button body and the stopper body, it is originally sufficient to plate only the outside surface. However, the shell cap is subjected to full surface plating because the one side plating is expensive as described above.
As will be described below, the present inventor found a novel method for subjecting metallic garment accessories to a surface electrolytic treatment using a bipolar phenomenon. Prior arts which disclose the plating method utilizing the bipolar phenomenon include Japanese Patent Application Public Disclosure (KOKAI) No. 2002-69689 A1 (Patent Document 1), Japanese Patent Application Public Disclosure (KOKAI) No. 2010-202900 A1 (Patent Document 2), and Japanese Patent Application Public Disclosure (KOKAI) No. 2013-155433 A1 (Patent Document 3). Patent Document 1 discloses a method for applying electroplating (bipolar plating) to fine powder having a particle size of 50 μm or less, using the bipolar phenomenon. Patent Document 2 discloses a method for producing an electrical contact comprising forming a noble metal plated film on a surface of a bipolar plated film by an electroless plating method. Patent Document 3 discloses a method for electroplating electronic/electric parts by indirectly supplying electricity, using the bipolar phenomenon. Therefore, all of these documents are irrelevant to the garment accessories which are attached to clothes and bags and which thus require improved fashionability and designability. Further, conventionally, in the industry of garment accessories, the bipolar phenomenon has been considered to be a cause of plating failure such as discoloration or nonuniformity of the plated film on the object to be plated.